1. Field of the Invention
This invention relates to a method for assaying an antibody against Chlamydia trachomatis for the diagnosis of C. trachomatis infection and a diagnostic preparation used therefor.
C. trachomatis is a species of the obligatory intracellular parasite which can be alive only in cells of a host. The multiplication cycle of the species is unique. Morphologically, an extracellular chlamydial elementary body (EB) is introduced by phagocytosis into cells of a host, wherein they form a vacuole, inclusion. They are in turn metamorphosed to a reticulate body (RB), which are multiplicative but not infective. The intracellularly multiplied RB is then metamorphosed to EB which ruptures the inclusion, breaks the cell membrane of the host and comes out of the cell. The EB is infective but not multiplicative. If infected with the EB, the infected person will suffer from eye or genital diseases such as eye trachoma, lymphogranuloma venereum (LGV), nongonococcal urethritis (NGU) and cervicitis.
Recently our attention has been drawn to C. trachomatis as one of the causative microorganisms for sexually transmitted diseases. In the United States of America, 3 to 10 million fresh cases per year of C. infections are reported. Concern with C. infections is increasing also in Japan as the actualities of the infection have increasingly been known.
2. Description of the Prior Art
The most sensitive serological diagnosis for C. trachomatis is by the indirect microimmunofluorescent antibody technique (the micro-IF technique) developed by Wang and Grayston (see "Trachoma and related disorders caused by chlamydial agents", Excerpta Medica, Amsterdam, pp. 273-288, 1971). However, the micro-IF technique has not yet been employed as a diagnostic method in clinical laboratories because of technical difficulties in its operation. Standard micro-IF technique needs purified elementary, bodies (EB) of 15 different C. trachomatis serotypes. The entire morphology or structure of a microorganism to be identified is needed for immunofluorescent reaction in the micro-IF technique. Therefore, modification or breakdown of the morphology or structure of EB cannot be employed. Since the EB is infectious and toxic, use of intact EB as an antigen material requires a special institution with a protective equipment from the infection. Accordingly, an antigen treated with a fixing agent such as formaldehyde or acetone is usually employed.
On the other hand, a recently developed enzyme immunoassay method (ELISA) has an advantage of being capable of treating many test specimens rapidly and in a simple manner. Reports on the assay of a C. trachomatis antibody using the ELISA have appeared, most of which, however, use EB of strain L2 of C. trachomatis, either intact or treated with SDS (sodium dodecyl sulfate) as an antigen material. As a result, non-specific reactions are known to occur due to the use of an antigen of lower purity, including cross reactions with a C. pneumoniae antibody and a C. psittaci antibody. This is mainly attributed to complicated antigenicity of C. trachomatis. Antigenicity of C. trachomatis is believed to be due to three classes of antigens, genus specific antigen, species specific antigen and serotype specific antigen. Lipopolysaccharides (LPS) are known to be a typical genus specific antigen, which is common in antigenicity with Re mutant LPS of some intestinal microorganisms.
In addition, as a typical species specific or serotype specific antigen is known the major outer membrane protein (MOMP) of C. trachomatis, which is reported to constitute about 60% of the C. outer membrane protein. However, the MOMP is known to have some genus specific epitope (Colett et al., Annu. Meet. Am. Soc. Microbiol., Washington, D.C., Abstract No. D-159, 1986). C. trachomatis outer membrane antigens other than the MOMP are predominantly genus specific antigens, but some have species specific antigenicity simultaneously. Sarcosyl-insoluble peptide having a molecular weight of approximately 59.5 Kdaltons is in the latter category.
As described above, antigenicity of C. trachomatis is very complicated. A C. trachomatis antibody in C. trachomatis infected patients is multifaceted corresponding to such complicated antigenicity of C. trachomatis and varies in its pattern depending upon the patients. Consequently, it is practically impossible to employ a specified single C. antigen for the assay of a C. trachomatis antibody. Therefore, the antigen material to be employed needs to be properly selected in order to achieve an highly precise and sensitive assay of an anti-C. trachomatis antibody while inhibiting non-specific reactions, including cross reactions with a C. pneumoniae antibody and a C. psittaci antibody.